1. ME 3351 Manufacturing Processes Tutorial 2 Eng. Ahmad Aljazea

2. What is a factory that performs casting operations usually called? Answer. A foundry.

3. Open mold & Closed mold

4. What is the difference between an open mold and a closed mold? Answer. An open mold is open to the atmosphere at the top; it is an open container in the desired shape which must be flat at the top. A closed mold has a cavity that is entirely enclosed by the mold, with a passageway (called the gating system) leading from the outside to the cavity. Molten metal is poured into this gating system to fill the mold.

5. Pattern and Core

6. What is the difference between a pattern and a core in sand molding? Answer. The pattern determines the external shape of the casted part, while a core determines its internal geometry.

7. What is meant by the term superheat? Answer. Superheat is the temperature difference above the melting point at which the molten metal is poured. The term also refers to the amount of heat that is removed from the molten metal between pouring and solidification.

8. Why should turbulent flow of molten metal into the mold be avoided? Answer. Turbulence causes several problems: (1) accelerates formation of oxides in the solidified metal, and (2) mold erosion or gradual wearing away of the mold due to impact of molten metal.

9. What is the continuity law as it applies to the flow of molten metal in casting? Answer. The continuity law, or continuity equation, indicates that the volumetric flow rate is constant throughout the liquid flow.

10. What are some of the factors affecting the fluidity of a molten metal during pouring into a mold cavity? Answer. Factors include: (1) pouring temperature, (2) metal alloy composition, (3) viscosity of liquid metal, and (4) heat transfer to the surroundings.

11. What does heat of fusion mean in casting? Answer. Heat of fusion is the amount of heat energy required to transform the metal from solid state to liquid state.

12. How does solidification of alloys differ from solidification of pure metals? Answer. Pure metals solidify at a single temperature equal to the melting point. Most alloys (exceptions are eutectic alloys) start to solidify at the liquidus and complete solidification at the solidus, where the liquidus is a higher temperature than the solidus.

13. What is a eutectic alloy? Answer. A eutectic alloy is a particular composition in an alloy system for which the solidus and liquidus temperatures are equal. The temperature is called the eutectic temperature. Hence, solidification occurs at a single temperature, rather than over a temperature range.

14. H.W Sand casting is which of the following types? (a) expendable mold, or (b) permanent mold. The upper half of a sand casting mold is called which of the following? (a) cope, or (b) drag. In casting, a flask is which one of the following? (a) beverage bottle for foundrymen, (b) box which holds the cope and drag, (c) container for holding liquid metal, or (d) metal which extrudes between the mold halves.

15. In foundry work, a runner is which one of the following? (a) channel in the mold leading from the downsprue to the main mold cavity, (b) foundryman who moves the molten metal to the mold, or (c) vertical channel into which molten metal is poured into the mold. Total solidification time is defined as which one of the following? (a) time between pouring and complete solidification, (b) time between pouring and cooling to room temperature, (c) time between solidification and cooling to room temperature, or (d) time to give up the heat of fusion. During solidification of an alloy when a mixture of solid and liquid metals are present, the solid-liquid mixture is referred to as whic h one of the following? (a) eutectic composition, (b) ingot segregation, (c) liquidus, (d) mushy zone, or (e) solidus.

16. Chvorinov's Rule states that total solidification time is proportional to which one of the following quantities? (a) (A/V)n, (b) Hf, (c) Tm, (d) V, (e) V/A, or (f) (V/A)2; where A = surface area of casting, Hf = heat of fusion, Tm = melting temperature, and V = volume of casting. A riser in casting is described by which of the following (may be more than one answer)? (a) an insert in the casting that inhibits buoyancy of the core, (b) gating system in which the sprue feeds directly into the cavity, (c) metal that is not part of the casting, (d) source of molten metal to feed the casting and compensate for shrinkage during solidification, and (e) waste metal that is usually recycled.

17. In a sand casting mold, the V/A ratio of the riser should be which one of the following relative to the V/A ratio of the casting itself? (a) equal, (b) greater, or (c) smaller.

18. A riser that is completely enclosed within the sand mold and connected to the main cavity by a channel to feed the molten metal is called which of the following (may be more than one)? (a) blind riser, (b) open riser, (c) side riser, and (d) top riser.